Monomers such as 2-carboxy-6-alkyl naphthalene ("CAN") and 2,6-dicarboxynaphthalene ("DCN") have been described as useful for the production of a variety of synthetic polymers. DCN has been described, for instance, as an alternative to terephthalate for the production of polyester films. See, e.g., Amoco Bulletin FA-4a R0686, Amoco Chemicals Co., Chicago, Ill. Films prepared from DCN can exhibit improved properties over those prepared from terephthalate, e.g., in terms of their glass transition temperature, tensile strength, gas permeability, and UV resistance.
Currently however, the use of such naphthalene-derived monomers is somewhat limited, partly in view of the high cost of preparing such monomers. Chemical synthesis of DCN is difficult and expensive, in that it typically requires extreme reaction conditions, and results in mixed oxidation products.
The production of organic compounds by means that include one or more biological conversions, i.e., biotransformations, has been proposed as a desirable alternative to the synthesis of compounds that are difficult and/or expensive to prepare chemically. Production by biological means is not always a feasible alternative however, in that it requires the fortuitous identification of naturally-occurring microorganisms or genetic material coding for enzymes capable of carrying out the desired biological conversions, or the creation of such microorganisms or genetic material, e.g., by mutagenesis or by recombinant DNA techniques.
A number of publications teach the degradation of aromatic compounds such as naphthalene or mono-substituted naphthalenes by biological means, e.g., using microorganisms capable of utilizing the compounds as a carbon source.
For instance, the bacterial oxidation of methyl substituents on aromatic rings is not uncommon. (See, e.g., Davey, et al., J. Bacteriol. 119:923-929 (1974), DeFrank, et al., J. Bacteriol. 129:1356-1364 (1977), and Williams, et al., J. Bacteriol. 120:416-423 (1974)). Usually, the methyl group is first oxidized to a carboxyl group, followed by a ring-opening step. (See, e.g., Williams et al., ibid., as well as Franklin, et al., Mol. Gen. Genet. 177:321-328 (1980), and Worsey, et al., J. Bacteriol. 124:7-13 (1975)). For substrates having more than one methyl group, typically only one such group is oxidized before the ring-opening step. (See, e.g., Franklin, et al., ibid., as well as Kunz, et al., J. Bacteriol. 146:179-191 (1981).
In some situations the ring-opening step may occur without the oxidation of the methyl group. See, e.g., Gibson, et al., Biochem. 7:2653-2662 (1968). For instance, Cane, et al., J. Gen. Microbiol. 128:2281-2290 (1982) describe a naphthalene dioxygenase that preferentially attacks the unsubstituted ring of 2-methyl naphthalene, in order to open the ring without oxidizing the methyl group.
Various plasmids have been identified as responsible for carrying genes coding for the enzymes involved in biological conversions. Of particular interest is a plasmid originally derived from Pseudomonas putida and designated the NAH7 plasmid, which carries, inter alia, two gene clusters that enable organisms bearing and expressing the plasmid to grow on naphthalene (nah+) as a sole carbon and energy source. (See, e.g., Yen, et al., Proc. Natl. Acad. Sci. U.S.A. 79:874-878 (1982), and Ensley, et al., Science 222:167-169 (1983)). U.S. Pat. No. 4,520,103 describes the use of the dioxygenase enzyme(s) of the "NAH7" plasmid for the microbial synthesis of indigo in indole-free media.
U.S. Pat. No. 3,340,155 describes a Streptomyces strain capable of converting a dialkyl naphthalene to a carboxy alkyl naphthalene ("CAN"). The conversion was quite slow however, e.g., a 120 hour incubation (about 5 days) for the conversion of 2,6-dimethyl naphthalene to the corresponding mono-carboxy acid. No recovery of the corresponding dicarboxy was described.
None of these references teach a microorganism or plasmid that is capable of oxidizing a dialkylnaphthalene in order to produce a dicarboxynaphthalene. The ability to prepare DCN by biological means, and/or to prepare CAN by more efficient biological means than previously described in the art, would be highly desirable, in that it would provide a relatively safe, efficient, inexpensive and convenient method of producing such monomers for use in polymer synthesis.